Simulated Helicopter Research Articles

Effect of helicopter noise spectra on annoyance of passengers

The annoyance of passengers to helicopter noise was investigated by exposing subjects to simulated helicopter noises in the NASA Passenger Ride Quality Apparatus. The passengers were subjected to the measured internal noise of the NASA Civil Helicopter Research Aircraft and to five filtered conditions of the noise, each at four noise levels. In addition, the subjects were given an incentive to identify a series of phonetically balanced (PB) words prior to recording their annoyance. Each subject experienced each condition at four levels ranging from 70 to 86 dBA. Removal of the gear-clash or other predominant-frequency components reduced the noise level and the annoyance ratings of the subjects. The annoyance was essentially the same for a given noise level with or without the gear-clash or other predominant-frequency components. For identical noise conditions, the annoyance was greater when the passenger-subjects were attempting to identify PB words.

Phase independence in low‐frequency pulse detection

The detectability of 10‐Hz pulse trains was measured for four pulse waveforms having identical Fourier series amplitude specta. One pulse was a simulated helicopter rotor pulse, the second was a polarity reversal of the rotor pulse, and the other two were random phase waveforms selected for low peak factor. The amplitude spectral envelope of the pulses had a broad maximum at 100 Hz. The detectibility was measured in a two interval forced choice task with 1‐s signals in continuous white noise. The results for two experienced and two naive subjects showed no detectibility differences between the pulses either across subjects or within single subjects, even though the sounds are clearly discriminable at suprathreshold levels and the waveform of the random phase pulses is similar to that of the masking noise. If the observed maximum detectibility difference between the pulses had attained 2 dB, it would have been significant at the 0.01 level. [Work supported by a grant to the Stanford‐NASA Ames Joint Institute for Aeronautics and Acoustics from the Army Air Mobility Research and Development Laboratory, Ames Directorate.]